The present invention relates to a light receiving element of a subject distance detector or rangefinder for a camera which receives light reflected from a remote object to be photographed, so as to detect the distance from the camera to the subject.
There are various kinds of active-type subject distance detecting devices which have light projecting means for projecting light to a remote subject to be photographed and light receiving means for receiving the light reflected from the subject to determine the distance between the subject and the subject distance detecting device. In such subject distance detecting devices, the subject distance can be determined according to the position at which the light reflected from the subject falls, because the reflected light returns at different incident angles according to the subject distance and so falls on correspondingly different positions.
Such an active-type subject distance detecting device comprises a pair of photoelectric elements with their associated converging lenses disposed in front of them. These photoelectric elements have different surface patterns which receive light from a remote subject to be measured to provide different photoelectric outputs. Although the photoelectric output varies as the intensity of incident light, which depends on variations in the intensity of incident light upon the photoelectric element, the brightness of subject, and ambient light, variations of the intensity of incident light can be cancelled by the provision of the pair of photoelectric elements with different light receiving surface patterns. Therefore, the subject distance detecting device can accurately detect the subject distance.
A typical example of such active-type subject distance detecting devices, as shown in FIG. 1, includes a pair of light receiving elements 1 and 2 disposed in a vertical direction and a pair of converging lenses 3 and 4 provided one individual to each light receiving element for converging incident light onto the respective light receiving elements. One of the pair of light receiving elements is formed with a sawtooth filter layer 7 on its light receiving surface to shield partially the light receiving surface from the light incident thereupon. The remaining light receiving element receives light over its entire light receiving surface. Light 5, 6 reflected from a remote subject, as is well known in the art, falls on the light receiving surface of each light receiving element at different positions in a direction shown by an arrowed line A-B according to the subject distance, because the incident angle of the light falling upon the light receiving surface varies depending upon the subject distance. If the intensity of light reflected from a subject is constant, the light receiving element 1 with the light shielding filter layer 7 provides a photoelectric output which is useful to provide subject distance information according to the position 5 on which the reflected light falls. However, the photoelectric output from the light receiving element generally varies depending upon the intensity of the incident light, even though the light falls at a constant incident angle and hence at the same location thereon. The intensity of light falling upon the light receiving element usually depends upon the reflectivity of the subject, the intensity of ambient light and so forth. Such variations of the intensity of incident light can be cancelled out by detecting also the intensity of the light reflected from the subject, by the light receiving element 2.
A problem with such subject distance detecting devices having a pair of light receiving elements is that the provision of two converging lenses one individual to each element gives rise to parallax effects due to the distance between the light receiving elements, as well as slight discrepancies of characteristics between the two light receiving elements and their associated converging lenses.